This invention relates to a combination anti-G and pressure suit, and in particular, to an immersion simulating anti-G and pressure suit intended for use by an aviator in a normal erect seated posture in a high performance aircraft.
High performance aircraft are capable of producing vertical accelerations exceeding the physiological capabilities of aviators. For example, sustained positive vertical acceleration of 4.5 G is the approximate upper human factor limit before loss of vision and loss of consciousness occur due to migration of body fluids, and particularly due to loss of blood pressure to the brain.
The limitation for negative vertical acceleration is about 3.0 G with risk of eye or brain damage. The limits are for gradual onset of acceleration, whereas many military aircraft are capable of rapid onset to vertical acceleration of 9.0 G or more in both positive and negative directions.
Anti-G suits in common current usage improve somewhat the human anti-G tolerance. Such suits utilize air pressure bladders in several parts of the lower body to counter body fluid migration and result in a G-tolerance improvement on the order of only about 1.0 G.
While using such suits, aviators are trained to bend forward and strenuously tension their stomach muscles and diaphragms in the so called "M 1 maneuver" to further increase their positive G tolerance to as much as +8 or 9 G. In addition, aviators are trained to monitor their peripheral vision since reduction of peripheral vision precedes the total loss of vision and consciousness.
The situation then is that a military aviator, wearing a conventional anti-G suit, while concentrating on attacking or evading an enemy, is obliged to divert his attention to decide whether his stomach and chest muscles are sufficiently strained to retain peripheral vision. The aviators physical limitations thus may very well be more critical to the result than the aircraft or weapon performance.
In prior art both liquid filled suits and liquid filled containers were intensively studied and tested both in flight and on human centrifuges. Acceleration tolerances of from 15 to 30 G were demonstrated. In principle, the migration of internal body fluids is prevented by matching external liquid pressures. In addition, liquid immersion provides neutral buoyancy, and body motions are not sensibly affected by the external acceleration forces. Liquid filled suits, on the other, hand transfer these forces to the limbs and body in addition to the acceleration forces of the liquid filled suit.
The great weight and bulk of these liquid systems was unacceptable for aircraft or rocket vehicles. Inability to inhale due to liquid pressures on the chest walls was the ultimate difficulty. All of the human centrifuge tests at the higher G levels were conducted with subjects holding their breath.
It is known from diving physiology that humans can easily hold their breath in free dives to 60 or more feet in a 1.0 G environment. This converts to 60/30 or two feet in a 30 G environment. However, breathing, as opposed to holding the breath at atmospheric pressure, is only possible to a depth of a few feet when immersed in a 1.0 G environment and only a few inches in a high G environment. The problem is that humans are incapable of expanding the chest and lungs against the acceleration-produced external liquid pressure. Prior art has attempted to deal with the respiration difficulties of liquid immersion by utilizing various pressure equalizing regulators such as the type used by skin divers.
One such prior art device is described in U.S. Pat. No. 3,137,290. The device is a liquid filled capsule which is intended to provide protection against G's and low pressure for crews of aircraft, manned space ships or other conveyances for humans. The liquid filled capsule is large enough to enclose the entire body of the crew member being protected, thereby providing the crew member's body with hydrostatic support from all directions. The liquid filled capsule is provided with external gas pressure means for stabilizing the liquid pressure at mouth level, a pressure equalizing regulator and a breathing mask.
Although the above-described and other similar immersion devices may offer improved G tolerance, it would appear that crew members would experience great difficulty in inhaling during positive acceleration and difficulty and some danger in exhaling during negative acceleration due to liquid pressures on the upper body. This problem can be of major concern when one considers that for aircraft usage the rate of change of acceleration can be many G per second. Therefore, the rate of change of respiration pressure is of the order of pounds per square inch per second. This is physically intolerable and may endanger the ear drums or lung tissue.
Another problem associated with fluid immersion is that the volume of the immersion fluid must vary to accommodate the expansion and contraction of the body during respiration without modifying the fluid pressure applied to the body. Following World War II, military anti-G suits evolved to their present form of pneumatic pressurization of parts of the lower body. Early versions of the anti-G suit were found to be valuable for wounded or shocked patients and have evolved into present day trauma or shock-suits. These have been found invaluable in restoring blood pressure and reducing fluid loss from wounds.
U.S. Pat. No. 2,667,459 discloses a ventilation system for spacesuits or other inflatable pressure garments.
U.S. Pat. Nos. 4,534,338 and 4,546,491 and others mention induced pressure changes and "milking action" in connection with anti-G suit operation.